Codelco, the world’s No. 1 copper producer, said it was still investigating the cause of the accident at Chuquicamata that left two workers dead when the vehicle they were driving collided with a giant mining truck.

Chile’s mining regulator said operations at Freeport’s El Abra partially resumed on Wednesday. Activities were halted on Tuesday after a worker died following an accident at its acid unloading terminal.

Century-old Chuquicamata produced 309,000 tonnes of copper in 2015, while El Abra, which is 51 percent owned by Freeport and 49 percent owned by Codelco, produced around 147,000 tonnes. (Reporting by Anthony Esposito & Fabian Cambero; Editing by W Simon and David Gregorio)